The basic overvoltage and overcurrent protection scheme used for a typical signal port is shown here. The TBU^® device is placed in series to block transient currents and provide voltage isolation. OVP1 limits the voltage at the input to the protected circuit and provides a path for transient current until the TBU device is triggered and transitions to the full blocking state. OVP1 may not be required if adequate protection is designed into a protected circuit. After the TBU HSP is triggered, OVP2 limits the voltage across the TBU device to a safe level and also provides a current path for the remainder of the transient event. A GDT can be chosen for OVP2 when used to protect high-speed communication lines such as DSL, Ethernet or LVDS. An MOV can be used for OVP2 for slower speed applications such as voice or RS-485. The OVP2 device should be chosen so that it does not trigger during power cross tests.